1. Field of the Invention
The invention relates generally to electrocardiography systems. More specifically, the invention relates to a Holter-type recorder capable of recording ECG wave forms in analog while simultaneously performing real-time analysis of the ECG signals and digital recording of the analysis results on cassette tape.
2. Prior Art
ECG ambulatory monitoring systems are used to obtain and analyze ECG wave forms, preferably obtained from a patient over an extended period of time. These systems usually comprise a recorder for collecting information from the patient related to the patient's ECG, and a scanner for analyzing the collected information. The scanner usually includes a playback deck for downloading information obtained by the recorder and a processing unit for analyzing the data and reporting analysis results. It has become increasingly important for scanners to be automated in order to limit the time in which it takes an operator to process, analyze and report data. It has also been increasingly important to increase the fidelity of the data collected and the accuracy, completeness and presentation of the analysis results.
Present recorders are generally designed for portable, long-term collection of electrocardiograph (ECG) data from a patient over an extended of time. The recordings made are subsequently used to detect abnormalities in the heart's electrical activity caused by a patient's routine daily activities or heightened emotional or physical states. The recordings are subsequently analyzed to form diagnoses, to assess the efficacy of treatments such as drug therapy, and to analyze pace-maker performance.
There are two basic types of ECG recording systems presently being used. The first is a "retrospective" type recording system which analyzes the collected data after completion of the collection phase. The second type is a "real-time" system which analyzes data as it is recorded. Retrospective systems typically record ECG data on a tape recorder during the collection phase, and subsequently analyze the data only after it has been downloaded into a scanner. Real-time systems typically record, analyze, and quantify data during the collection phase, and the analysis information is merely played back by the scanner once downloaded thereinto. Data collected on a real-time system is generally recorded on an electronic medium in digital form instead of on magnetic tape.
In either system, the recording unit is generally capable of amplifying ECG signals which are received from the patient through a plurality of input leads (which are attached through electrodes to various points on the patient's chest) which input either to a tape recorder (retrospective) or an electronic storage device (real-time). Real-time systems generally further include a microprocessor in conjunction with the electronic storage device for analyzing the ECG signals. Both the real-time and the retrospective type recording systems are designed to interface with a scanner, either through a magnetic tape reader, or an electronic interface, to allow downloading of the collected information for analysis, editing, storage, and/or reporting as necessary or desired.
Real-time and retrospective recording systems each have their drawbacks. For example, real-time recording systems which analyze and quantify ECG signals as they are being monitored, are limited in the amount of data they can store by the size limitations imposed by the electronic memory. Although there have been attempts to limit this problem by compressing raw data through computer algorithms, or by limiting the data stored (e.g., storing only information on ECG signals generated by aberrant heartbeats) these efforts have been less than completely successful in resolving the problem. For example, it is well known that compression algorithms can cause distortions in the data which become apparent as reduced signal fidelity when the data is later retrieved for use. Further, since it is often desirable for analysis purposes in a comprehensive clinical evaluation to be able to review all ECG wave forms as recorded over an entire monitoring period (often 24 hours), present real-time systems are often found to be less than desirable. This tradeoff of low reproducibility of signal fidelity for an increased in memory capacity is a major limitation on prior art real-time recording systems.
Retrospective recording systems, although having virtually no data storage limitations during a 24 hour ECG recording period, nevertheless suffer in the fidelity of their reproduced signal after being downloaded into a scanner. This is because the scanners often read the recordings at speeds of 60 to 240 times their actual recorded speed. These high speed play backs tend to limit fidelity by decreasing the frequency range of the recordings, and also tend to cause inaccuracy in time tracking of the tape due to tape biasing and/or misalignment of the tape on the play back head during high speed play back, and/or tape stretching due to high speed stopping and starting of the tape during analysis.
For example, when analyzing how well a heart responds to a signal from an implanted pace-maker, an inaccuracy in the timing between the pace-maker signal and the apparent response of the heart can make the difference between the perceived heart response being interpreted as physiologically acceptable or unacceptable.
Another major drawback with retrospective recording systems is the time required to rewind, download and analyze the recorded data by the scanner system, and the further time necessary to compile and generate reports based on the data.
There therefore exists a need in the art to develop a recorder which can perform real-time analysis of ECG signals from a patient over a long period of time without the necessity of compressing the data to accommodate the storage medium used. Further, there exists a need in the art to develop an ECG recorder which allows for rapid reporting of pertinent summary information usable by medical workers for purposes of early review and preliminary diagnoses.